1. Field of the Invention
The present invention relates generally to the field of devices and methods for orthodontic treatment, as well as devices useful for maintaining the corrected positions of a patient""s teeth after treatment, and more particularly to an improved system of springs useful for returning teeth to desired, treated positions in cases where the corrected orthodontic results have relapsed after treatment.
2. Statement of the Problem
In the field of orthodontics, particularly the area involving the commercial fabrication of orthodontic appliances by orthodontic support laboratories, it is a long-established and well-known practice to conform polymerizing materials into shapes that passively conform to a patient""s teeth, gums or palate. Such xe2x80x9ccast massxe2x80x9d-type appliances are typically formed from materials such as a dimethacrylate paste activated by a benzoyl peroxide-amine, a self polymerizing methyl methacrylate composition or light curable compositions such as a dimethycrylate paste activated by a camphor quinine, or other heat-softening thermoplastic urethane resins, all of which demonstrate rigid mechanical properties once cast and cured. FIG. 1 is a top perspective view of an example of such an appliance.
It is also common practice for orthodontic laboratories to embed various types of active or passive metallic devices into such cast mass-type appliances during the casting and subsequent curing process. The metallic devices are anticipatorily pre-positioned within the cast mass by a laboratory technician to contact a patient""s teeth in desirable ways once the appliance is placed in the patient""s mouth. The metallic devices act to urge the teeth to move in desirable ways, including repositioning the teeth into desired or corrected positions and orientations as part of an orthodontist""s overall treatment plan.
Such active appliances, when adapted to the upper teeth normally span the top of the patient""s mouth in contact with the palate and extend into close proximity to the lingual gingival margins of some or all of a patient""s upper teeth. When such an appliance is being fabricated for application to the lower arch, the configuration of the cast mass is significantly relieved compared to the upper configuration. This is to provide clearance for the tongue, and therefore, lower versions of this type of appliance are generally trimmed and contoured to the lateral and anterior aspects of the lingual of the lower dental arch.
The metallic devices that are typically embedded in such an orthodontic appliance are elastically loaded or stated differently, they are capable of storing energy. The metallic devices are deflected by the mal-occluded teeth or in a sense loaded as the appliance is positioned and fully seated in the mouth. The corrective force that directs the teeth into desirable positions is the dissipation, over time, of the energy stored in such deflected metallic devices.
Treatment using such cast mass-type appliances inherently involves the primary corrective forces being generated from the lingual side of the teeth, and therefore such forces are outwardly directed. Such forces are typically simple, single-vector forces that are intended to tip the crown of inwardly canted teeth outward.
Inwardly-acting forces directed to the outside (i.e. the labial and buccal surfaces of the teeth) can also be applied by this type of appliance. To accomplish this, orthodontic lab technicians will typically fabricate a cast mass-type appliance exhibiting a section of hard, stainless steel wire, with its two ends embedded in the cast mass as shown in FIG. 1.
The mid-span of the resilient stainless steel wire is supported as the wire extends outward between teeth on either side of the patient""s arch. The mid-span section of the wire spans the outer surfaces of the anterior teeth and is commonly referred to as a xe2x80x9clabial bowxe2x80x9d. A typical cast mass-type appliance as described, containing embedded metallic devices that act on both the inside and outside surfaces (i.e. with a labial bow on the outside of the teeth) of some or all of the teeth constitutes one common and well-known type of orthodontic appliance.
As can be appreciated, the interaction of the loaded spring devices on the inside of the teeth may push the crowns outward until such time that they contact the labial bow. Over the course of treatment, the crowns may contact the labial bow but nonetheless still exhibit an undesirable rotation. It is the continued pushing of the springs on the teeth from the inside, against the labial bow, that will slowly rotate the tooth to a desirable corrected position.
To best contrast the advantages and benefits of the present invention, it is necessary to describe the well known limitations and shortcomings of current cast-mass-type appliances. First, it must be appreciated that the physiological response elicited from current cast mass-type appliances proceeds very slowly, consuming many months of treatment time. The second and most notable shortcoming of the current-design cast mass-type appliance that the present inventive system of springs favorably improves upon is that such appliances have no control whatsoever over the important consideration of alignment of the roots of the teeth. The movement of the teeth accomplished by current cast-mass-type appliances can be likened to uprighting a xe2x80x9cstick stuck into sandxe2x80x9d, where the portion of the stick buried in the sand rotates around an unknown center of resistance with its lower extremities moving through the sand in one direction and its upper extremities moving in the opposite direction.
The absence of the ability to control the true location of an uprighted tooth is a major drawback and thus the use of cast mass-type appliances is limited. Nonetheless, cast mass-type appliances serve as useful adjuncts to other primary treatment methods (e.g., conventional braces) used to accomplish treatment goals during the active phase of orthodontic treatment.
To further illustrate the nature of the limitations of current cast mass-type appliances, it should be understood that the metallic devices embedded in cast mass-type appliances are capable of simple, single-vector correction of the inclination of the crowns of lingually-disposed teeth in an outward direction. The outer bow feature of such an appliance serves as a stop, limiting the correction to a roughly desired inclination. All of the limitations of such appliances described above are generally recognized by orthodontists and orthodontic laboratory technicians. In particular, such appliances are recognized, as being incapable of generating the more complex couple-type forces required to bodily move the roots of teeth through the supporting bone. The term xe2x80x9ccouplexe2x80x9d is defined as the relationship between any two forces acting on a body where in combination, those forces tend to cause that body to rotate about a point. In contrast to a couple, the simple single-vector corrective forces generated by current cast mass-type appliances act only on the crown of a tooth and serve only to tip a tooth about its centroid.
The term xe2x80x9ccentroidxe2x80x9d in the dental lexicon describes the theoretical center of resistance of a tooth""s root as it is rotated through its alveolar bone structure in response to a single force applied, over time, to some point on its visible crown. The location of the center of resistance/center of rotation (i.e. the centroid) is hidden well below the gingival margin of a tooth at a theoretical point within the root. This biological centroid can again be thought of as being similar to the neutral rotation point as in the example above describing a stick being uprighted in sand.
Even though useful for some treatment objectives, orthodontists do not use such cast mass-type appliances as a primary corrective regimen. This is due to the inability of such appliances to bodily translate teeth through supportive bone as described. Such appliances are therefore typically relegated to serving as adjuncts to other primary labial methods (e.g., conventional xe2x80x9cbracesxe2x80x9d) as may be required for an individual patient""s treatment.
A second type of orthodontic laboratory-produced appliance is also well known and is commercially fabricated in the same general manner and from generally the same group of materials as the appliance described above. This second type differs from the first in that rather than serving during the active tooth-moving phase of treatment, it serves to immobilize teeth in desirable positions, orientations and relationships after the active phase of treatment has ended. Such appliances are commonly referred to as xe2x80x9cretainersxe2x80x9d and differ from the first type of appliance described in that the metallic devices embedded in them are configured to hold teeth statically in their treated positions. Such appliances further serve to support or mechanically shelter the teeth against destabilizing forces or imbalances that may exist between the inwardly directed forces of the patient""s facial musculature, the outward pressures of the tongue, as well as the deleterious effects of unanticipated post-treatment skeletal growth. This second type of appliance is successfully used for retention of the teeth because it""s various shortcomings and limitations described above do not reduce its effectiveness in holding and retaining the teeth.
Retainers are typically prescribed for a patient by the dentist or orthodontist at the completion of regular orthodontic treatment. The attending orthodontist expects the retainer to maintain the results achieved during the active phase of treatment. The patient is instructed to begin wearing his or her retainer immediately after the braces are removed and to continue its use for a prescribed period of time thereafter. A patient then may remain in a post-treatment retention phase for one year or two years or even longer. In some cases, the attending orthodontist may prescribe that the post-treatment retention continues indefinitely. Indefinite (i.e. permanent) retention is indicated in particular cases where the patient""s unique functional and physiological attributes clearly predispose the teeth for relapse.
Regarding orthodontic treatment generally, the orthodontic literature contains substantial references to the loss of the functional and aesthetic gains of orthodontic treatment after a period of time. See, Melrose et al., xe2x80x9cToward a Perspective on Orthodontic Retention?xe2x80x9d, American Journal of Orthodontics and Dentofacial Orthopedics, vol. 113, no. 5, pp. 507-514 (May 1998); Al Yami et al., xe2x80x9cStability of Orthodontic Treatment Outcome: Follow-Up Until 10 Years Postretention,xe2x80x9d American Journal of Orthodontics and Dentofacial Orthopedics, vol. 115, no. 3, pp. 300-304 (March 1999); Jarabak, Technique and Treatment with Lightwire Edgewise Appliances, vol. II, pp. 1143 et seq. (Mosby 1972); Graber, Orthodontics Principles and Practice (W. B. Saunders Company, 1972). Melrose et al. lament that there are no methods or reliable statistical means of determining a patient""s propensity for post-treatment relapse, and no tools or reliable means to determine the correct minimum period of retention that will preclude relapse. The work by Al Yami et al. statistically paints a picture where perhaps only 67% of orthodontic cases can expect to remain stable for a 10-year post-treatment period. Graber even goes so far as to say that the fundamental step of attempting to retain teeth creates an artificial and unstable gnathologic condition and in the final analysis, it is necessitated by failure to achieve the primary orthodontic goals of treatment to a stable, functional occlusion.
Relapsed cases are also referred to as xe2x80x9cfailed casesxe2x80x9d or xe2x80x9ccollapsed casesxe2x80x9d and occur when individual teeth or groups of teeth move into undesirable positions and undesirable relationships. There are multiple causes for such collapsed cases outside of periodontal compromise, including loss of anchorage due to the teeth being precariously positioned relative to the underlying bone, the compressive effects of interference resulting from unanticipated post-treatment growth of the face and particularly the mandible, the continued presence of destructive swallowing or sucking habits, abnormally taut facial musculature, fundamental misjudgment on the part of the orthodontist in the planning of treatment, misdiagnosis of the nature of the original malocclusion and non-cooperation in a case where a patient fails to wear his or her retainer as prescribed or fails to follow other instructions of the orthodontist.
A typical collapsed case will typically begin with the loss of normal interproximal contacts of the lower anterior teeth, usually due to a gradual loss of proper torque of the of the upper anterior teeth leading to a general decrease in arch length. The resulting compressive forces act to compress and push the lower front teeth together. Lacking normal contact with adjacent teeth, sometimes combined with interference from opposing teeth, one tooth or another will rotate or tip out of alignment and then slip in front of, or behind an adjacent tooth. Once the combinative support and stability provided by normal gnathological interdigitation and normal interproximal contacts of the lower anterior teeth are lost, all of the lower anterior teeth may begin to tip or splay inward as a group. Likewise in the upper arch, ideal tooth positioning that may have been achieved and supported during the active phase of treatment may degrade once the orthodontic hardware is removed. The upper front teeth may tip as a group in response to an imbalance between the outward forces of the tongue and the inward forces of the facial musculature.
Such cases are very discouraging for a patient when the hard-won and aesthetically-pleasing results of treatment are lost. Collapsed cases are an all too common disappointment for the orthodontic patient who sees the expense and inconvenience of his or her treatment as culminating in failure. The present invention provides a new and important option to patients whose treatment has failed. The present invention serves well to restore the orthodontic gains achieved during the active phase of treatment. In the past, a patient""s options were limited to simply accepting the failure of his or her treatment, or considering undergoing the process of orthodontic treatment for a second time.
3. Solution to the Problem
The present invention involves a novel system of spring devices that are fabricated from new materials that are activated and adapted to the teeth in new ways. The present invention is a system of springs capable of loading the alveolar bone which supports the roots of the teeth in ways that elicits a fundamentally different type and rate of physiological response, allowing teeth to move much more quickly, thus allowing orthodontic treatment to be accomplished much more quickly than with any current methodologies. In combination, these new features and capabilities overcome the various limitations of the standard cast mass-type of appliance as well as open up the cast mass-type appliance for new and important treatment roles. The present inventive system of springs in combination with the cast mass-type appliance enable improved treatment methodologies for practitioners. The current invention enables the venerable cast mass-type appliance to see expanded application. Its new applications are directed toward both the fundamental challenges faced by orthodontists during active treatment, as well as the problem of correcting failed cases.
To illustrate one of the advantages of the current invention, it must be appreciated that most conventional orthodontic appliances are considered to be xe2x80x9cfixedxe2x80x9d in that they are permanently attached to the teeth and remain in place in the mouth until removed by the orthodontist. As a group, cast mass-type appliances are considered to be xe2x80x9cremovablexe2x80x9d appliances because the patient can routinely put them in and take them out. In most cases, treatment with removable appliances typically proceeds with the appliance being worn only during the evenings and during sleep. Special cases may require that such appliances be worn more, particularly in the early stages of treatment, but generally, a patient always has the option of removing them. This allows the patient to avoid the many inconveniences and socially self-conscious aspects of orthodontic treatment (e.g., the unwanted xe2x80x9cmetal mouthxe2x80x9d look). Removable appliances provide many practical advantages compared to fixed appliances and such advantages benefit the patient, the orthodontist and his staff. As can be appreciated, a removable cast mass-type appliance incorporating improvements of the present invention and thereby rendering it capable of achieving the primary objectives of orthodontic treatment is a development with tremendous treatment-related and commercial impact. Even though many patients stoically tolerate the nuisance-aspects of their orthodontic treatment such as its negative impact on the ability to speak normally and self-image issues, as well as eating and oral hygiene problems, the latitude of being able to not wear orthodontic devices during work, school and special social settings is extremely desirable.
Considering the present invention and its capacity for use as a means to correct failed or collapsed cases, patients whose original orthodontic treatment has collapsed are inherently older, and they may be of an age where they have entered the work force and/or started a career. One demographic model includes image-conscious young professional people whose desire for orthodontic correction is countered by a reluctance to repeat their earlier treatment, which would likely consume two to three years and would involve the negative stigma of xe2x80x9cadult braces.xe2x80x9d Individuals falling into such a group would very likely find the feature of xe2x80x9cremovabilityxe2x80x9d as a very important consideration and thus they may be much more apt to consider repeating orthodontic treatment if given the option of a treatment modality that may progress only during the evenings and during sleep. Further, the removable cast mass-type appliance inherently discloses less orthodontic hardware on the visible front teeth. Compared to conventional braces, the labial bow and one or more springs of the present invention are much less unsightly.
For these many reasons, the present invention represents an important improvement in the current standard of orthodontic care. The present invention has significant commercial potential in that it represents a new treatment modality that addresses basic shortcomings of traditional braces-type orthodontic treatment, and it has attributes that accommodates important lifestyle considerations for young adults needing orthodontic correction.
This invention provides a method and apparatus for orthodontic treatment employing a cast mass-type appliance with a labial bow and combinations of labial and lingual springs to produce multiple coupled forces on all or selected teeth. The lingual spring has a stem embedded in the appliance and a plurality of pairs of activation loops at its active, tooth-contacting end, which extend laterally outward from the longitudinal axis of the stem. The labial spring has a pair of opposing lateral wings for attachment to a labial bow, and one or more rabbit ears extending selectively either occlusally or gingivally along the labial surface of the tooth. The orthodontist may selectively pre-activate the springs so that the lingual spring exerts a labially-directed force from the lingual side of a tooth and the labial spring exerts a lingually-directed force from the labial side of a tooth. In addition to such activations, both the springs positioned on the inside and positioned on the outside of the teeth are typically simultaneously further activated in complementary ways to correct undesirable tooth rotations. The system of springs of the present invention are thereby typically configured and activated to load or stress the underlying alveolar bone in ways that would not normally occur. The stresses produced by such coupled orthodontic forces on the crown of the tooth that are then translated into the supporting bone are different than any of the forces that the bone would normally encounter in its natural process of accommodation of changes in its functional loading. Therefore, those forces are forces that the tooth""s periodontal membrane and the surrounding region of bone are not evolutionarily equipped to accommodate or mechanically resist.
The biological impact of the present inventive system of springs should also be considered. All living tissue, including the tissues of the human body perpetually strive to maintain a sort of structural homeostasis, in balance with both systemic self-generated mechanical forces and external mechanical forces that are constantly changing. In particular, the bony structures of the human body are constantly engaged in the process of adapting to changes in loading. It is well known that the bony structures of the human body also change in response to genetically triggered growth signals, and that bones grow to a genetically pre-determined extent.
The process whereby bone adapts to maintain a dynamic balance with changing structural demands is a naturally occurring response. For example, humans subjected to prolonged zero gravity in space experience loss of bone mass, whereas individuals whose vocation involves excessive loading of certain bones see those bones change in shape and increase in mass in response to those increased loads.
When observing the human mandible as it relates to orthodontics, it can be seen that unlike most other human bones, the mandible, exhibits a remarkable capability to remodel. For example, the mandible accommodates the arrival of molars at age 6 and again at age 12 by significantly lengthening in the horizontal axis relative to the vertical. Its overall shape will adapt and accommodate and comply with the position and angle of the opposing maxilla as well as the skeletal structure of the face and so on as it strives to maintain a functional balance in harmony with surrounding living structure. During growth of the individual as well as after skeletal maturity, the mandible clearly responds to a wide variety of reformative forces acting upon it.
The alveolar bone supporting both the upper and lower dentition is a particularly adaptive structure that participates in the maintenance of a dynamically balanced occlusion. The occlusion is influenced by the geometry of the temporal mandibular joint and vice versa. Each root of each tooth is encapsulated within a protective, elastic periodontal membrane, which in turn is positioned within the supportive alveolar bone and even though a mechanically structural system, the position of each tooth should be understood as imminently malleable. Together, all of the teeth continually vie for balance with the opposing and the adjacent teeth as well as with the inwardly and outwardly directed forces of the adjacent soft tissues.
The dynamic balance between all of the oral structures and the skeletal realities of all of the bony structures below the floor of the cranium, and indeed the cranium itself must be appreciated as a non-rigid, constantly adapting and malleable natural living mechanical system.
To best understand the present invention, it is necessary to first appreciate the symphony of inter-accommodative mechanical forces endlessly operative in the living structure, striving to maintain functional balance, and more particularly that the teeth and the alveolar bone participate in this dynamic balancing. A distinction must be made however regarding the nature of the forces that drive this process. One quality that these forces share is that they can all be considered as natural forces; not because they occur in living tissue but because the are all relatively large, single-direction vectors of compression or tension or bending that trigonometrically occur by default between the geometry of the structural members (the bones, the muscles, cartilaginous and connective tissues) involved.
To further characterize these natural forces, teeth must accommodate the intrusive/compressive forces of occlusion and mastication. The mandible itself must withstand a rather intense bending moment as is required to shear and crush food. The powerfully constrictive musculature between the sides of the skull and the mandible load all of the adjacent bony structures in compression. The forces that must be accommodated by structures such as the skull, the mandible and the alveolar bone supporting the teeth are considered to be functional forces and importantly, all of these living structures are of course ideally designed through the process of evolution to accommodate these naturally occurring forces associated with growing and living.
The current array of orthodontic armamentarium in worldwide use today is based on mechanical force delivery models capable of imparting forces that are actually similar to the simple, naturally occurring single-vector forces described above. Generally, the current array of orthodontic armamentarium acts to achieve orthodontic correction by the application of single vector corrective forces to a tooth or groups of teeth in a lineal sequence. For example, as described herein, prior art cast mass-type of appliances attempt to push on the crown of a tooth to desirably tip that tooth. Other types of appliances currently used within orthodontics attempt correction by selectively exerting similar pushing, pulling or twisting forces on teeth to urge them into desirable positions and orientations.
As can be appreciated from the foregoing, the underlying alveolar bone reacts to the introduction of such simple, single vector corrective forces as if those forces are like the naturally occurring functional forces described above. This then elicits a physiological response and the alveolar bone will slowly accommodate those forces producing tooth movement. The bone is in a sense being xe2x80x9ctrickedxe2x80x9d into responding to the forces introduced by the conventional orthodontist as if they were the same as the naturally occurring forces that are accommodated for living balance.
The present invention achieves a rate of orthodontic response (i.e. the desirable repositioning of the roots of individual teeth) through the alveolar process that is approximately five times faster than what is considered to be a normal rate of tooth movement achieved during conventional orthodontic treatment. The markedly faster rate of orthodontic correction observed in treatment using the present invention is completely devoid of the pathological and sometimes necrotic sequella that is traditionally thought to be associated with such exceedingly rapid tooth movement.
For example, in the early years of orthodontics, very high forces were used to move teeth and such forces and such excessive forces typically resulted in resorption (shortening or blunting) of the roots of the teeth being moved, and associated trauma to the periosteal tissues and the surrounding bone. In controlled clinical settings, the present inventive system of springs used in conjunction with the cast mass-type appliances achieves markedly faster rates of tooth movement without any of these problems, and without any discomfort to the patient.
A physiological analysis of the basis of such rapid response, in light of current understandings of bone growth and bone remodeling as well as metallurgical advances incorporated into the present invention follows below.
In contrast to current orthodontic armamentarium, the present inventive system of springs delivers a resultant root-moving force vector that is always a xe2x80x9cvector compositexe2x80x9d of at least three or more distinctly separate, but closely coupled force vectors. By locally loading the living alveolar bone with a complex array of closely coupled but distinctly non-coplanar force vectors, the bone is structurally loaded in ways that are clearly outside of the category of forces that it is naturally designed to accommodate. Even though the resulting vector-sum of forces generated by the present invention may be identical in direction and amplitude to a simple, single vector force as is generated by the current orthodontic armamentarium, the fact that the present invention achieves that resultant vector by combining at least 3 multiple vectors seems to elicit a new and profoundly different type of response in the underlying bone. It is felt that this is the key to such remarkably fast, yet safe and painless rates of physiological response from the bone.
To better illustrate the way that the alveolar bone responds to the present invention, consider that the orthodontic literature is replete with research describing a conventional model of tooth movement. It is well known that a process called the xe2x80x9costeoclast/osteoblastxe2x80x9d mode of tooth movement is operative in response to conventional orthodontic forces. The xe2x80x9costeoclast/osteoblastxe2x80x9d mode of tooth movement describes a process where the resorption of bone is thought to occur in the direction of tooth movement and the process of deposition of bone occurs, which is the filling-in of new bone behind a tooth as it moves in response to a gentle, continuous force. Such tooth movement involves the movement of the root as well as its periodontal membrane through the bone.
Studies show that orthodontic treatment using the present inventive system of springs achieves a somewhat different mode of root translation. It involves the translation of a living assembly that is thought to involve the root, the periodontal membrane and importantly, the region of alveolar bone locally adjacent to, and surrounding the root and the periodontal membrane This living assembly can be considered as moving together as one physiologic unit. The interface between the moving physiologic unit and the surrounding alveolar bone is thought to extend significantly further away from the root than the conventional osteoclast/osteoblast model of tooth movement. Orthodontic treatment using the present inventive system of springs can perhaps be thought of as moving one region of tooth-supporting alveolar bone through a larger region of stationary alveolar bone.
All living organisms are the product of billions of years of evolution and billions of years of structural accommodation of the dynamic loads experienced by individuals. Only by the skilled intervention of orthodontists can the living structures of the mandible and maxilla be loaded with such concentrated and complex loading patterns so as to trigger such a different type of physiological response.
As described above, even though the net vector resultant of the multi-coupled forces generated by the present invention may be in a logical direction for treatment, it nonetheless is composed of a minimum of three distinct non-coplanar vector forces. Loading and stressing the underlying bone in this unnatural way produces an extraordinary and generally unobserved rapidity to the physiological tooth-moving response.
To further optimize the coupled forces that are carried to the underlying alveolar bone through contact of the teeth with the present inventive system, the springs can be formed of a chromium-cobalt alloy. The present invention further benefits from the desirable properties of this alloy through certain metallurgical treatments resulting in the alloy exhibiting its maximum work-hardened and heat-treated hard condition. Even though this alloy is known to be useful in unrelated orthodontic applications when used in generally larger diameters, the present invention employs the alloy in its hardest condition and in small diameters. The unique properties that result through the use of the alloy and its conditioning, further combined with the novel physical configurations of the formed configurations combinatively produce a highly optimized gentle and continuous physiological force that is ideally calibrated to elicit maximum response in the alveolar bone when loaded in the complex, multiple vector manner produced by the present invention.
These and other advantages, features, and benefits of the present invention will be more readily understood in view of the following detailed descriptions and the drawings.